Motor control apparatus, disk apparatus and acceleration detection device

ABSTRACT

A motor controlling device includes an acceleration detector for detecting an acceleration of a motor; a motor driver for supplying a driving current to the motor; a heat quantity calculator for calculating a heat quantity generated in the motor at least based on an output from the acceleration detector; and a motor controller for controlling the motor driver based on the heat quantity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No.09/778,421, entitled “MOTOR CONTROL APPARATUS, DISK APPARATUS, ANDACCELERATION DETECTION DEVICE”, which was filed on Feb. 7, 2001, andwhich claims priority to Japanese Application No. 2000-028759, filed onFeb. 7, 2000, both of which are incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to a motor control device for preventing atemperature rise of an optical disk apparatus including the motorcontrol device, based on a predicted temperature rise of a motor or theapparatus including the motor, by calculating the quantity of heatgenerated by the motor; and a disk apparatus including such a motorcontrol device.

BACKGROUND OF INVENTION

Motors have conventionally been incorporated in various types ofapparatus. Motors rotate a driven target by causing an electric currentto flow through a motor coil and thus generating a rotation force (i.e.,torque) corresponding to the size of the electric current. When a motoris rotated at a constant speed, it is sufficient to generate a torquecorresponding to a load on a bearing or the like. Accordingly, only asmall amount of current is required. However, when the speed of rotationneeds to be rapidly accelerated or decelerated, a torque correspondingto the magnitude of the acceleration of deceleration is required. Insuch a case, an electric current of an amount corresponding to therequired torque needs to flow. The heat generated in the motor coil bythe flow of an electric current increases in proportion to the square ofthe size of the electric current. Therefore, the motor coil in anapparatus incorporating a motor which is rotated with rapid accelerationor deceleration generates a huge amount of heat, and accordingly it isrequired to prevent a temperature rise caused by the heat generation.

For example, a disk apparatus, for performing information recording andreproduction by rotating a disk as a recording medium while moving arecording head, sometimes repeats a seek operation frequently. The seekoperation means the operation of moving the recording head to a desiredposition over the recording medium at high speed. During the seekoperation, the rotation speeds of a head transporting motor fortransporting the recording head and a disk motor for rotating the diskneed to be rapidly changed. These motors generate a huge quantity ofheat. Such heat generation caused during the seek operation raises thetemperature of the disk and the elements of the disk apparatus to alevel exceeding the temperature at which the disk and the elements canwithstand. Solutions of this problem of temperature rise have beenproposed.

Japanese Laid-Open Publication No. 6-119008, for example, discloses asystem including a temperature sensor in an optical disk apparatus,which operates as follows. The temperature of the optical disk apparatusis detected. When the temperature of the optical disk apparatus exceedsa preset temperature, the operation of the optical disk apparatus isrestricted, so that an excessive temperature rise is prevented.

In order to reduce the cost of components and the number of steps ofassembly which are required by the provision of a temperature sensor, orin order to detect the temperature at a position at which it isdifficult to directly attach a temperature sensor, technology forpredicting the temperature at a desired position by calculation has beenproposed. Japanese Laid-Open Publication No. 7-153208, for example,discloses a system for predicting, by calculation, a temperature rise ofa voice coil motor (VCM), as a head transporting motor, based on a valueof the electric current commanded to the VCM.

FIG. 10 shows a conventional magnetic disk apparatus 101 for predictinga temperature rise by calculation. The magnetic disk apparatus 101includes a servo controller 118 and a disk enclosure (hereinafter,referred to as the “DE”) 102. The servo controller 118 includes a VCMcontrol section 135. The VCM control section 135 includes a RAM 122, apositioning control section 115, and a temperature detection section 114for predicting the temperature of a VCM 106 (described below). The DE102 includes a disk motor 103, a spindle 104, a magnetic disk 105, theVCM 106, and a magnetic head 107. The magnetic head 107 is moved in aradial direction of the magnetic disk 105 by the VCM 106. Thus, themagnetic head 107 is properly positioned.

In the RAM 122, various data is stored. The data to be stored in the RAM122 includes, for example, iv (value of the electric current commandedto the VCM 106), ΔQv1 (heat quantity corresponding to the temperaturerise), ΔQv2 (heat quantity spontaneously radiated), Qv (heat quantity ofa measurement target), and Tv (temperature of the measurement target).The measurement target is an element, the temperature of which is to bemeasured. The data stored in the RAM 122 can be updated. A timer (softtimer) is set in the RAM 122. A ROM (not shown) included in the VCMcontrol section 135 has various data already stored therein. The datastored in the ROM includes, for example, K (constant), 0 (constant ofthermal resistance), Cv (thermal capacity of the measurement target), Te(environmental temperature), ts (sampling time), a (constant) and b(constant).

In the disk apparatus 101 having the above-described structure, thetemperature detection section 114 predicts the temperature of the VCM106 by calculation in the following manner.

The VCM control section 135 interrupts a usual seek control every 66μsec. (i.e., sampling time ts), and detects the position of the magnetichead 107 and updates the value iv.

Next, the temperature detection section 114 multiplies the square of thevalue iv by coefficient K and sampling time ts. Then, ΔQv2 is subtractedfrom ΔQv1. The resultant value is integrated (i.e., Qve←Qv+ΔQv1−ΔQv2) toobtain the heat quantity Qv of the measurement target. Thus, thetemperature Tv of the measurement target is detected (Tv=Qv/Cv).

The above-described processing is performed every 66 μsec. (i.e.,sampling time ts) to detect the temperature Ts. The detected temperatureTs is stored in the RAM 122. When the seek operation is performed, thetemperature Tv is read from the RAM 122, and the seek operation iscontrolled based on the temperature Tv.

When the detected temperature Tv is higher than a reference value, thestart of the seek operation is delayed in accordance with thetemperature Tv. Thus, the temperature rise is restricted.

A delay amount D′, by which the start of the seek operation is delayed,is expressed by D′=a·Tv−b as the linear function of the temperature Tv(where a and b are constants stored in the ROM).

The delay amount D′ is set as follows in accordance with the temperatureTv. The reference value for the temperature is T1′. In a region whereTv≦T1′, D′ is set as 0; and in a region where Tv>T1′, D′ is set asa·Tv−b.

Accordingly, when the temperature Tv is equal to or lower than thereference value T1′, the seek operation is started immediately uponreceiving an instruction to seek. When the temperature Tv is higher thanthe reference value T1′, the start of the seek operation is delayed bythe delay amount which is set in proportion to the temperature Tv. Inthis manner, the temperature rise of the VCM 106 is restricted, and thusthe VCM 106 is protected against overheating.

However, the conventional magnetic disk apparatus 101 has a problem inthat the precision of calculation of the heat quantity ΔQv1 issignificantly poor.

The heat quantity ΔQv1 can be found by multiplying the square of theamount of the electric current flowing through the coil of the VCM 106by a constant (coil resistance and the time during which the electriccurrent flows). In the above-described conventional apparatus 101, thecalculation is performed using the value of the electric currentcommanded to the VCM 106 instead of the amount of the electric currentitself. This is done with the premise that the amount of the electriccurrent and the value of the electric current commanded to the VCM 106are proportional with respect to each other. However, these two are notnecessarily proportional to each other.

FIG. 11 is a graph illustrating the relationship between the value ivand the actual amount of the electric current i of a general motordriver IC. As shown by the chain line in FIG. 11, the conventionalcalculation method assumes that the value iv and the actual amount ofthe electric current i are proportional to each other (i=c·iv). However,there is actually a range of values iv, which is referred to as the“dead zone”. In the dead zone, the amount of the electric current iwhich is output is zero regardless of the value iv. The size of the deadzone greatly varies among individual ICs, so that the value iv and theactual amount of the electric current i are not proportional to eachother. Furthermore, in a range where the value iv is larger than aconstant iv0, the relationship between values iv and i (i.e.,i=c1·iv+d1) becomes i=c2·iv+d2. Therefore, the relationship betweenvalues iv and i exhibits non-linearity in that the proportionalityfactor (c1 and c2) varies in accordance with the range of the value iv.Additionally, constants c1, c2, d1 and d2 greatly vary among individualICs. The value i can vary significantly with respect to the same valueiv, depending on the IC.

The driver IC detects the value i and the feedback control by monitoringvoltages at both ends of a detection resistor provided in series to themotor. However, the resistance of the detection resistor is set to be assmall as about 0.1 Ω in order to minimize the motor driving loss.Therefore, the influence of errors of the line resistances in the IC orthe like is not negligible. As a result, it is difficult to raise theprecision of current detection.

For the above-described reasons, the electric current icalc calculatedby the conventional method based on a value iv1 has a large error withrespect to an actual electric current ireal. The heat quantity ΔQv1calculated from the amount of the electric current icalc differssubstantially from the heat actually generated in the VCM 106. Thus, theprecision of temperature prediction is very poor.

Since the VCM 106 is controlled by the result of temperature predictionhaving such a poor precision, the following inconveniences occur: thestart of the seek operation is not delayed although the actualtemperature exceeds the reference value T1′, which results inoverheating or destruction of the VCM 106; and the start of the seekoperation is delayed although the actual temperature is sufficientlylower than the reference value T1′, which lowers the performance of themagnetic disk apparatus 101.

A direct detection of the actual electric current i at a high precisionrequires a complicated structure and undesirably raises the cost ofcomponents and the number of steps of assembly.

SUMMARY OF INVENTION

According to one aspect of the invention, a motor controlling deviceincludes an acceleration detector for detecting an acceleration of amotor; a motor driver for supplying a driving current to the motor; aheat quantity calculator for calculating a heat quantity generated inthe motor at least based on an output from the acceleration detector;and a motor controller for controlling the motor driver based on theheat quantity.

In one embodiment of the invention, the acceleration detector includes amovement distance indicating device for detecting a prescribed movementdistance of the motor; and a timer for counting a time period requiredfor the motor to move the prescribed movement distance. The accelerationdetector calculates the acceleration based on an output from themovement distance indicating device and an output from the timer.

In one embodiment of the invention, the heat quantity calculator storesthe relationship between the acceleration and the heat quantity, andcalculates the heat quantity at least from the acceleration which isoutput from the acceleration detector based on the relationship.

In one embodiment of the invention, the beat quantity calculatorcalculates the heat quantity at least based on a first value obtained bymultiplying a square of the acceleration by a first constant.

In one embodiment of the invention, the motor controlling device furtherincludes an inertia determiner for determining an inertia of a load whenthe motor is driven, wherein the first constant is changed by an outputfrom the inertia determiner.

In one embodiment of the invention, the acceleration detector calculatesa prescribed rotation distance by multiplying the prescribed movementdistance by a prescribed integer, and the heat quantity calculatorcalculates the heat quantity at least based on a sum of a first valueobtained by multiplying a square of the acceleration by a first constantand a second value obtained by multiplying the prescribed rotationdistance by a second constant.

In one embodiment of the invention, the motor controlling device furtherincludes an inertia determiner for determining an inertia of a load whenthe motor is driven, wherein the first constant is changed by an outputfrom the inertia determiner.

In one embodiment of the invention, the accelerator detector includes amovement distance indicating device for detecting a prescribed movementdistance of the motor and generating a pulse at each prescribed movementdistance, a timer for counting a time duration between generations ofthe pulses, and a speed calculator for calculating a speed of the motorfrom the time duration each time the motor moves a prescribed rotationdistance which is obtained by multiplying an integer the prescribedmovement distance. The acceleration detector calculates the accelerationfrom the speed.

In one embodiment of the invention, the prescribed rotation distance isequal to a value obtained by multiplying by an integer the rotationdistance corresponding to one rotation of the motor.

In one embodiment of the invention, the acceleration detector includes amovement distance indicating device for generating a pulse each time themotor moves a prescribed angle D. A speed calculator for calculating arotation speed N(n) of the motor by expression (1) each time themovement distance indicating device generates the n'th pulse. Adifferential calculator for calculating an i'th acceleration A(i) byexpression (2) each time j pulses are generated:N(n)=D/Δtp(n)  expression (1)A(i)=(N(j·i)−N(j·(i−1)))/Δt(i)  expression (2)

-   -   where n, i and j are positive integers, Δtp(n) is a time        duration between the time when the n'th pulse is generated and        the time when the (n−1)th pulse is generated by the movement        distance indicating device, and Δt(i) is a time duration between        the time when the (j·i)th pulse is generated and the when the        (j·(i−1))th pulse is generated by the movement distance        indicating device.

In one embodiment of the invention, j is a value obtained by multiplyingby an integer the number of pulses which are generated by the movementdistance indicating device while the motor rotates once.

In one embodiment of the invention, the acceleration detector includes adigital filter for receiving the rotation speed N(n) of the motor andoutputting an average rotation speed N′(n). The differential calculatorcalculates the acceleration A(i) using the average rotation speed N′(n)instead of the rotation speed N(n).

In one embodiment of the invention, the digital filter calculates theaverage rotation speed N′(n) by expression (3):N′(n)=(N(n)+(m−1)·N′(n−1))/m  expression (3)

-   -   where m is a positive integer.        In one embodiment of the invention, the motor controller        includes a temperature calculator for calculating at least one        of a temperature change of the motor and a temperature change of        a driven target of the motor based on the heat quantity        calculated by the heat quantity calculator, and a current        controller for restricting a driving current which is output by        the motor driver. The temperature change exceeds a prescribed        threshold level, and the motor controller sets a restriction        value of the driving current.

In one embodiment of the invention, the restriction value is changed inaccordance with an amount by which the temperature change exceeds theprescribed threshold level.

According to another aspect of the invention, a disk apparatus includesa motor for rotating a disk; an optical head for recording informationon the disk or for reproducing information from the disk; a motor driverfor supplying a driving current to the motor; a motor controller forsetting the driving current; a speed calculator for calculating arotation speed of the motor; and a determiner for determining whether ornot the rotation speed of the motor is within a range in which recordingof information to the disk or reproduction of information from the diskby the optical head is possible. When the determiner determines that therotation speed of the motor is within the range, the motor controllerrestricts the driving current.

In one embodiment of the invention, the motor controller sets therestriction value of the driving current to be higher as an intendedrotation speed of the motor increases.

In one embodiment of the invention, the motor controller sets therestriction value of the driving current to be higher than therestriction value at the time of a start of an acceleration of themotor, before the rotation speed of the motor is maintained at theintended rotation speed.

In one embodiment of the invention, the disk apparatus further includesan acceleration detector for detecting an acceleration of the motor, aheat quantity calculator for calculating a heat quantity of the motor atleast based on the acceleration which is output by the accelerationdetector, and a temperature calculator for calculating a temperaturechange in a prescribed area of the disk apparatus based on the heatquantity. The determiner determines whether or not the temperaturechange is equal to or less than a prescribed threshold level. Thedeterminer determines that the temperature change is equal to or lessthan the prescribed threshold level and that the rotation speed of themotor is within the range, the motor controller restricts the drivingcurrent. When the determiner determines that the temperature change ismore than the prescribed threshold level, the motor controller restrictsthe driving current.

In one embodiment of the invention, the motor controller sets therestriction value of the driving current to be higher as an intendedrotation speed of the motor increases.

In one embodiment of the invention, the motor controller sets therestriction value of the driving current to be higher than therestriction value at the time of a start of an acceleration of themotor, before the rotation speed of the motor is maintained at theintended rotation speed.

According to still another aspect of the invention, a disk apparatusincludes a motor for rotating a disk; an optical head for recordinginformation on the disk or for reproducing information from the disk; amotor driver for supplying a driving current to the motor; a motorcontroller for setting the driving current; a synchronous clockgenerator for generating a synchronous clock based on a reproductionsignal which is read from the disk by the optical head; a speedcalculator for calculating a rotation speed of the motor; and adeterminer for determining whether or not the rotation speed of themotor is within a range in which generation of the synchronous clock ispossible. When the determiner determines that the rotation speed of themotor is within the range, the motor controller restricts the drivingcurrent.

In one embodiment of the invention, the motor controller sets therestriction value of the driving current to be higher as an intendedrotation speed of the motor increases.

In one embodiment of the invention, the motor controller sets therestriction value of the driving current to be higher than therestriction value at the time of a start of an acceleration of themotor, before the rotation speed of the motor is maintained at theintended rotation speed.

According to still another aspect of the invention, a disk apparatusincludes a motor for rotating a disk; an optical head for recordinginformation on the disk or for reproducing information from the disk; amotor driver for supplying a driving current to the motor; a motorcontroller for setting the driving current; a speed calculator forcalculating a rotation speed of the motor; and a determiner fordetermining whether or not the optical head is recording information tothe disk or reproducing information from the disk, and whether or notthe rotation speed of the motor has changed. When the determinerdetermines that the optical head is not recording information to thedisk or reproducing information from the disk and that the rotationspeed of the motor has changed, the motor controller restricts thedriving current.

According to still another aspect of the invention, a disk apparatusincludes a motor for rotating a disk; an optical head for recordinginformation on the disk or for reproducing information from the disk; amotor driver for supplying a driving current to the motor; a motorcontroller for setting the driving current; a head transporting devicefor transporting the optical head to a prescribed position above thedisk at which recording or reproduction of information is to beperformed by the optical head; a speed calculator for calculating arotation speed of the motor; and a determiner for determining, during aseek operation in which the head is transported, whether or not therotation speed of the motor is within a range in which informationrecording to the disk or information reproduction from the disk by theoptical head is possible. When the determiner determines that therotation speed is within the range, the motor controller restricts thedriving current so that the rotation speed of the motor is constant fora prescribed time period.

According to still another aspect of the invention, a disk apparatusincludes a motor for rotating a disk; an optical head for recordinginformation on the disk or for reproducing information from the disk; amotor driver for supplying a driving current to the motor; a motorcontroller for setting the driving current; an acceleration detector fordetecting an acceleration of the motor; a heat quantity calculator forcalculating a heat quantity of the motor at least based on theacceleration which is output by the acceleration detector; a temperaturecalculator for calculating a temperature change in a prescribed area ofthe disk apparatus based on the heat quantity: and a determiner fordetermining whether or not the temperature change is equal to or morethan a prescribed threshold level. When the determiner determines thatthe temperature change is equal to or more than the prescribed thresholdlevel, the motor controller restricts the driving current.

According to still another aspect of the invention, a speed detectiondevice includes a movement distance indicating device for generating apulse each time a motor moves a prescribed movement distance; a timerfor counting a time duration between generations of the pulses; and aspeed calculator for calculating a speed of the motor based on the timeduration each time the motor rotates a prescribed rotation distancewhich is obtained by multiplying by an integer the prescribed movementdistance. The prescribed rotation distance is equal to a value obtainedby multiplying by an integer a rotation distance corresponding to onerotation of the motor.

According to still another aspect of the invention, an accelerationdetection device includes the above-described speed detection device. Anacceleration is calculated from the speed.

Thus, the invention described herein makes possible the advantages ofproviding a motor control apparatus for preventing inconveniences causedby overheating while guaranteeing high performance by controlling amotor operation at appropriate timing with a superb heat quantitycalculation function, a disk apparatus including such a motor controlapparatus, and high, precision acceleration detection device and speeddetection device.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a structure of a motorcontroller and an optical disk apparatus including the motor controlleraccording to a first example of the present invention;

FIG. 2 is a timing diagram illustrating an example of a change in therotation speed of a disk motor in the optical disk apparatus accordingto the first example;

FIG. 3 is a timing diagram illustrating a seek operation when apredicted temperature change value is relatively small according to thefirst example;

FIG. 4 is a timing diagram illustrating a seek operation when apredicted temperature change value is relatively large according to thefirst example;

FIG. 5 is a timing diagram illustrating the relationship between thepredicted temperature change value and the commanded current valueaccording to the first example;

FIG. 6 is a schematic diagram illustrating a structure of a motorcontroller and an optical disk apparatus including the motor controlleraccording to a second example of the present invention;

FIG. 7 is a timing diagram illustrating an example of a change of therotation speed when a disk motor in the optical disk apparatus isaccelerated or decelerated in repetition according to the secondexample;

FIG. 8 is a timing diagram illustrating a seek operation when anintended rotation speed is relatively high according to the secondexample;

FIG. 9 is a timing diagram illustrating a seek operation when anintended rotation speed is relatively low according to the secondexample;

FIG. 10 is a schematic view illustrating a conventional optical diskapparatus; and

FIG. 11 is a diagram illustrating the relationship between the commandedcurrent value and the driving current of a motor in a motor driver IC.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described by way ofillustrative examples with reference to the accompanying drawings.

EXAMPLE 1

FIG. 1 is a schematic diagram illustrating a structure of an opticaldisk apparatus 1 according to a first example of the present invention.

The optical disk apparatus 1 includes a motor control device 27, aturntable 3 on which an optical disk 2 is placed, a disk motor 4 forrotating the turntable 3 and the optical disk 2, an optical head 5, aguide shaft 6 for supporting the optical head 5 so as to be movable in aradial direction of the optical disk 2, a head transporting motor 7 forsupplying a driving force to transport the optical head 5 supported bythe guide shaft 6 to a desired radial position above the optical disk 2,a chassis 9, a head signal processing circuit 22, a synchronous clockgenerator 23, and a signal processor 24.

The disk motor 4 includes a stator section 30 having a motor coil 29which is supplied with an electric current and thus generates anelectromagnetic field, and a rotor section 32 having a ring-shapedmagnet 31. The magnet 31 includes positive and negative magnetic polesprovided alternately in a circumferential direction. The disk motor 4includes a sensor section 10 a, which is an element of a movementdistance indicating device 10 described below. A rotation distance ofthe disk motor 4 is detected by the sensor section 10 a. The disk motor4 is a DC motor.

The optical head 5 records information by directing a laser beam to theoptical disk 2, and reads information by using a laser beam directed toand reflected by the optical disk 2.

The chassis 9 is formed of a resin. On the chassis 9, the disk motor 4,the guide shaft 6, the head transporting motor 7 and the like are fixed.

The motor control device 27 includes an acceleration detector 15, a heatquantity calculator 16, a motor driver 17, a motor controller 21, and aCPU 25 having an inertia determiner 26.

The acceleration detector 15 includes a timer 11, a speed calculator 12,a digital filter 13, a differential calculator 14, and a waveformrectifier 10 b, which is an element of the movement distance indicatingdevice 10 described below.

The motor controller 21 includes a commanded current value generator 18,a current controller 19, and a temperature calculator 20.

When the optical disk 2 is inserted into the optical disk apparatus 1 bya loading mechanism (not shown), the optical disk apparatus 1 determinesthe type of the optical disk 2 and records information to, or reproducesinformation, from the optical disk 2. The optical disk 2 can be aread-only optical disk such as, for example, a CD-ROM or a DVD (digitalversatile disk)-ROM, or a recordable/readable optical disk such as, forexample, a PD or a DVD-RAM.

The movement distance indicating device 10 is an encoder for outputtinga pulse (rectangular wave) each time the disk motor 4 rotates by a unitangle D. The movement distance indicating device 10 includes the sensorsection 10 a including a hole element and the like, and the waveformrectifier 10 b for rectifying the shape of an output signal of thesensor section 10 a. The sensor section 10 a is usually integrated withthe disk motor 4, but may be provided separately from the disk motor 4.When integrated with the disk motor 4, the sensor section 10 a islocated so as to face the magnet 31 of the rotor 32 of the disk motor 4,and thus detects the strength of the positive and negative magneticfields which change as the rotor section 32 rotates. The sensor section10 a outputs the detected strength as a sine wave. The waveformrectifier 10 b is an element of the acceleration detector 15, and thusrectifies the sine wave output from the sensor section 10 a into arectangular wave and outputs the rectangular wave. A movement distance(i.e., rotation angle) of the disk motor 4 is calculated by counting thepulses output by the movement distance indicating device 10. Forexample, in the case where the encoder (i.e., movement distanceindicating device 10) outputs six pulses during one rotation of the diskmotor 4, the unit angle D by which the disk motor 4 rotates each time apulse is output is 60 degrees. Therefore, the rotation angle can befound by multiplying the number of pulses counted by 60 degrees.

The timer 11 includes a function of counting time using an operationalclock of the CPU 25. The timer 11 counts the number of clock cyclesbetween pulses output by the waveform rectifier 10 b, using the pulse asa trigger to count a time duration between the pulses; and outputs thetime duration to the speed calculator 12, the differential calculator 14and the heat quantity calculator 16 at respective appropriate timing.

Each time the movement distance indicating device 10 generates a pulse,the speed calculator 12 obtains, from the timer 11 a time duration Δtpfrom the immediately previous pulse generation. Thus, the speedcalculator 12 calculates a speed N(n) by expression (1) shown below(where n is a positive integer). The speed N(n) is a speed calculatedwhen the n'th pulse is generated, and the speed N(n−1) is a speedcalculated when a pulse immediately before the n'th pulse is generated.D is the unit angle, by which the disk motor 4 moves each time a pulseis generated, as described above.N(n)=D/Δtp(n)  (1)

The digital filter 13 calculates an average speed N′(n) from the speedN(n) based on expression (3) shown below.N′(n)=(N(n)+(m−1)·N′(n−1))/m  (3)

In the above, m is a constant defining the cut-off frequency of thedigital filter 13. Usually, when the disk motor 4 rotates at a constantspeed, the time duration between pulses should theoretically beconstant, and also the time duration Δtp used by the speed calculator 12for the calculation of the speed N(n) should always be the same.However, in reality, the time duration Δtp is not the same due to, forexample, a positional error of magnetic poles of the magnet 31 providedin the disk motor 4, even when the disk motor 4 rotates at a constantspeed. Such an error can produce undesirable high frequency noise in thecalculation result of the speed N(n). This error is reduced by thedigital filter 13. As a result, the prediction precision of thetemperature change obtained by calculation can be improved.

The differential calculator 14 calculates an acceleration A(i) from theaverage speed N′(i) output by the digital filter 13, based on expression(4).A(i)=(N′(j·i)−N′(j·(i−1)))/Δt(i)  (4)

In the above, i is a positive integer and indicates that the calculationis the i'th calculation to obtain an acceleration. In this example, j isa prescribed integer and indicates that A(i) is calculated at every j'thpulse. Δt(i) is the time duration between the (j·i)th pulse and the(j·(i−1))th pulse which are output by the movement distance indicatingdevice 10. From the (j·i)th pulse and the (j·(i−1))th pulse, the averagespeeds N′(j·i) and N′(j·(i−1)) are calculated. The acceleration detector15 outputs the calculated acceleration A(i) of the disk motor 4 to theheat quantity calculator 16.

The heat quantity calculator 16 calculates a heat quantity E(i)generated in the disk motor 4 in accordance with expression (5).E(i)=α·A(i)² ·Δt(i)+Tm·j·D+E(i−1)  (5)

In the above, α (first constant) is calculated by expression (6).α=R·J ² /Kt ²  (6)

In the above, R is the resistance of the motor coil 29, J is the inertiaof the optical disk 2 and the rotor section 32 of the disk motor 4, Ktis the torque constant of the disk motor 4, and Tm (second constant) isa torque loaded on the bearing of the disk motor 4. Tm may be set basedon any of various resistance elements instead of a friction resistanceon the bearing. Also in the above, j is the number of pulses generatedby the movement distance indicating device 10 between the time when theheat quantity E(i−1) is found and the time when the heat quantity E(i)is found, and j·D is referred to as the “rotation distance” of the diskmotor 4.

By substituting E1(i) into the first term and E2(i) into the secondterm, E1(i) can be represented by expression (7). E1(i) is obtained bymultiplying the square of the acceleration by the first constant.E 1(i)=R·(J·A(i)/Kt)² ·Δt(i)  (7)

In the above, J·A(i) is obtained by multiplying the inertia by theacceleration. Therefore, J·A(i) indicates the motor torque based on theequation of motion. Since the motor torque and the motor driving currentare substantially proportional to each other (proportionality factor:torque constant Kt), J·A(i)/Kt indicates the amount of the motor drivingcurrent. Accordingly, the heat quantity E1(i) is obtained by multiplyingthe square of the motor driving current by the resistance of the motorcoil 29 and the time duration Δt(i).

E2(i) as the second term of expression (5) is obtained by multiplyingthe torque Tm loaded on the bearing by j·D. E2(i) is obtained by afriction-generated heat quantity which is caused by, for example, thefriction at the bearing of the disk motor 4. The third term ofexpression (5) represents the heat quantity E(i−1) found by the (i−1)thcalculation for the heat quantity by the heat quantity calculator 16.

The heat quantity E(i) generated by the heat quantity calculator 16 isfound by adding the heat quantity E(i−1) to the newly generated heatquantity E1(i) of the motor coil 29 and the friction-generated heatquantity E2(i).

Since the DC motor torque and the motor driving current aresubstantially proportional to each other, the heat quantity generated bythe motor coil 29 can be calculated by expression (7) with a highprecision. Even in the case of a motor which does not have such aprecisely proportional relationship, the heat quantity generated by themotor coil can be calculated as long as the heat quantity generated bythe motor coil and the acceleration have a relationship which can berepresented by a certain expression. For example, even when the motortorque and the motor driving current have a nonlinear relationship, theheat quantity generated by the motor coil can be found by expression(8). The motor torque is calculated from the acceleration by theequation of motion. The motor driving current is calculated by the motortorque.E 1(i)=R·I(i)² ·Δt(i)  (8)

In the above, I(i) is the motor driving current.

The motor driver 17 supplies an electric current to the disk motor 4 inaccordance with the commanded current value which is input by thecommanded current value generator 18.

The commanded current value generator 18 receives, from the CPU 25, anintended position of the optical disk 2 at which information is to berecorded or reproduced. The commanded current value generator 18calculates the rotation speed of the disk motor 4 which is required torecord or reproduce information at the intended position. Then, thecommanded current value generator 18 compares the rotation speed of thedisk motor 4 at that point and an intended rotation speed. When the twospeed do not match each other, the commanded current value generator 18instructs acceleration or deceleration required to make the speeds matcheach other. The commanded current value generator 18 also generates an“commanded current value” which represents the amount of the electriccurrent which is commanded by the motor controller 21 to the motordriver 17 as the amount to flow through the disk motor 4 at the time ofacceleration or deceleration. The commanded current value is output tothe motor driver 17.

The current controller 19 changes the commanded current value generatedby the commanded current value generator 18 and thus restricts theamount of the driving current supplied by the motor driver 17 to thedisk motor 4. The current controller 19 receives, from the CPU 25, arestriction instruction flag which indicates whether the driving currentis to be restricted or not. When the driving current is to berestricted, the current controller 19 receives data indicating arestriction range and operates in accordance with the data command.Restriction of the driving current suppresses the heat generation in thedisk motor 4 and thus suppresses a temperature rise.

The temperature calculator 20 calculates a k'th predicted temperaturechange value T(k) of a control target. The control target may be thedisk motor 4 or any element of the optical disk apparatus 1, thetemperature of which is to be controlled. The k'th predicted temperaturechange value T(k) is calculated by expression (9) based on the (k−1)thpredicted temperature change value T(k−1), the time duration Δts(k)between the time when T(k) is found and the time when T(k−1) is found,and the heat quantity E(i).T(k)=exp{−Δts(k)/τ}·T(k−1)+Kc·E(i)  (9)

In the above, k, τ and Kc are positive constants. The predictedtemperature change value T(k) is not the temperature change of thecontrol target itself, but is the temperature difference between thecontrol target and the environment of the control target. Moreprecisely, the calculation of expression (9) has the premises that thethermal capacity of the environment is sufficiently large and that thetemperature change of the environment is slower than the temperaturechange of the control target. Among the constants, τ and Kc representthe time constant and the thermal capacity of the control target,respectively. The first term of the right side of expression (9)represents a temperature fall by spontaneous heat radiation, and thesecond term represents a temperature rise by the heat quantity E(i). Thevalues of τ and Kc are obtained by experiment and are stored in the ROM(not shown) in the motor control device 27. Elements which arecontrolled by the motor control device 27 can include, for example, thedisk motor 4 and driven targets of the disk motor 4 such as the opticaldisk 2.

The motor controller 21 controls the motor driver 17 based on aninstruction from the CPU 25.

The head signal processor 22 converts a signal read by the optical head5 from the optical disk 2 and outputs the converted binary signal intothe synchronous clock generator 23 and the signal processor 24.

The synchronous clock generator 23 includes a PLL circuit (not shown)and generates a clock signal which is synchronized with a binary signaloutput from the head signal processor 22. In the case where the opticaldisk 2 is of a CLV (Constant Linear Velocity) system for controlling thelinear velocity of the optical disk 2 at the recording or reproductionposition to be substantially constant, the rotation speed of the diskmotor 4 at which a synchronous clock can be generated varies inaccordance with the radial position at which the recording orreproduction is performed. A synchronous clock can be generated within aprescribed range of rotation speeds around a rotation speed which ispredetermined for each radial position. The recording or reproductioncan be performed only after generation of a synchronous clock becomespossible. During a seek operation for changing the recording orreproduction position, the rotation speed of the optical disk 2 isrequired to be put within the rotation speed range in which asynchronous clock can be generated.

The signal processor 24 performs demodulation, error correction and thelike based on a clock signal generated by the synchronous clockgenerator 23 and a binary signal output by the head signal processor 22.Then, the signal processor 24 generates a data signal and thusreproduces information recorded on the optical disk 2. The signalprocessor 24 also outputs an information signal to be recorded based onthe clock signal to the optical head 5 and thus records the informationon the optical disk 2.

The CPU 25 controls the entire optical disk apparatus 1 based on theprograms and data which are stored in advance in the ROM (not shown).For example, the CPU 25 exchanges commands with, or transfers data to, ahost apparatus 28 through a SCSI or other interface (not shown). The CPU25 also controls various elements of the optical disk apparatus 1including the motor controller 21. For example, immediately beforestarting a seek operation based on an instruction from the hostapparatus 28 to reproduce or record information, the CPU 25 obtains apredicted temperature value of a prescribed position (for example, inneror outer circumference of the optical disk 2) from the temperaturecalculator 20. Then, based on the predicted temperature value, the CPU25 sends an instruction to the commanded current value generator 18 andthe current controller 19. Thus, the CPU 25 controls the driving currentof the disk motor 4.

The operation of the inertia determiner 26 is executed by the CPU 25 asa program stored in the ROM (not shown). The inertia determiner 26determines the difference in the diameter of different optical disksbased on the data signal which is output from the signal processor 24and thus calculates an inertia. Then, the inertia determiner 26 outputsthe inertia to the heat quantity calculator 16 as the constant α (firstconstant).

The acceleration detector 15, the heat quantity calculator 16, the motordriver 17, the motor controller 21, the head signal processor 22, thesynchronous clock generator 23, the signal processor 24, and the CPU 25may be provided on a circuit board.

The motor control device 27 and the optical disk apparatus 1 includingthe motor control device 27 operate, for example, in the followingmanner.

First, the CPU 25 initializes each of variables which are output by theacceleration detector 15 and the heat quantity calculator 16 to aninitial value (i.e., the O'th value). Specifically, the speed N(0) foundby the speed calculator 12, the average speed N′(0) found by the digitalfilter 13, the acceleration A(0) found by the differential calculator14, and the heat quantity E(0) found by the heat quantity calculator 16are all set to 0. The CPU 25 temporarily sets the initial value of thefirst constant α which is used by the heat quantity calculator 16 forcalculating the heat quantity E(i) to, for example, a value calculatedin advance using the inertia of a 12-cm disk (expression (6)). The CPU25 also sets the initial value T(0) of the predicted temperature changevalue found by the temperature calculator 20 to 0. Thus, theinitialization of each of the variables is completed.

Then, the CPU 25 causes the timer 11 to start counting time. Based on aninstruction of the CPU 25, the commanded current value generator 18causes the disk motor 4 to rotate at a predetermined intended rotationspeed. In order to realize this, the commanded current value generator18 compares the intended rotation speed and the rotation speed of thedisk motor 4 at that time, and outputs a commanded current value inaccordance with the difference of the two speeds, to the motor driver17. Since the disk motor 4 is not in operation when the disk apparatus 1has just started, the commanded current value generator 18 supplies amaximum possible commanded current value to the motor driver 17, so thatthe disk motor 4 can be rotated at a maximum rotation acceleration.Thus, the motor driver 17 supplies an electric current to the disk motor4, and the disk motor 4 starts rotating. When the rotation speed reachesthe intended rotation speed, the commanded current value generator 18reduces the commanded current value to a value which is necessary torotate the disk motor 4 at a constant speed, so that the disk motor 4keeps rotating at the intended rotation speed.

The CPU 25 controls the driving of the head transporting motor 7 so asto move the optical head 5 to a prescribed position above the opticaldisk 2. The head transporting motor 7 may be controlled by a motorcontrol device which is similar to the motor control device 27 providedfor controlling the driving of the disk motor 4.

Simultaneously with the start of the rotation of the disk motor 4, theCPU 25 causes the optical head 5 to start reading a signal from theoptical disk 2. The read signal is converted into a binary signal by thehead signal processor 22 and is input to the synchronous clock generator23. The synchronous clock generator 23 can only generate a synchronousclock within a prescribed rotation speed range (which changes inaccordance with the radial position at which the recording orreproduction is performed). Immediately after the start of the diskmotor 4, the rotation speed is too low to generate a synchronous clock.When the rotation speed of the disk motor 4 increases and reaches theprescribed rotation speed range, the signal processor 24 can generate adata signal from the binary signal which is output from the head signalprocessor 22 and the synchronous clock. Thus, the optical disk apparatus1 is ready to perform recording or reproduction. The type of the diskmounted on the optical disk apparatus 1 is determined based on the datasignal generated by the signal processor 24, and various parameters andthe like required to control the determined type of disk are set.

The inertia determiner 26 re-sets the first constant α used by the heatquantity calculator 16 for calculating the heat quantity E(i) to thevalue determined for each disk type. In the case of an 8-cm disk, forexample, the first constant α is re-set to the value calculated byexpression (6) with the value of j being changed in accordance with theinertia of the 8-cm disk.

When the disk motor 4 starts rotating and the movement distanceindicating device 10 starts outputting pulses, the speed calculator 12,the digital filter 13, the differential calculator 14, and the heatquantity calculator 16 start calculating the speed N, the average speedN′, the acceleration A and the heat quantity E, respectively.

FIG. 2 is a timing diagram illustrating the rotation speed of the diskmotor 4 (FIG. 1) which increases at a constant acceleration. FIG. 2shows the speed N(n), the average speed N′(n) and the acceleration A(n)in relation to the pulses generated by the movement distance indicatingdevice 10.

The speed calculator 12 obtains the time duration Δtp(n) between thepulses generated by the movement distance indicating device 10 from thetimer 111 and calculates the speed N(n) in accordance with expression(1) each time a pulse is generated. The obtained speed N(n) generallyincludes an error with respect to the actual speed, due to thepositional error of the magnetic poles of the magnet 31 or the like. Thedigital filter 13 removes a high frequency component as the errorincluded in the speed N(n) and thus obtains the average speed N′(n) inaccordance with expression (3). The differential calculator 14calculates the acceleration A(i) in accordance with expression (4) basedon the average speed N′(i) and the time duration Δt(i). Here, j=1, andsince the acceleration A(i) is found each time a pulse is generated,i=n. If the acceleration A(i) was calculated using the speed N(n)instead of the average speed N′(n), the error with respect to the actualspeed would be significantly larger than the error shown in FIG. 2.Using the average speed N′(n) instead of the speed N(n) to obtain theacceleration A(i), the calculation error can be significantly reduced.Therefore, the heat quantity can be calculated and the temperature risecan be predicted sufficiently accurately.

Returning to FIG. 1, the heat quantity calculator 16 uses the obtainedacceleration A(i) to calculate the heat quantity E(i) of the disk motor4 in accordance with expression (5). Expression (5) considers the heatquantity generated in the motor coil 29 which is found from theacceleration A(i) as well as the friction-generated heat quantity whichis caused by the load on the bearing of the disk motor 4. Thus, theprecision of the calculation of heat quantity is improved. Since theacceleration A(i) is calculated each time a pulse is generated by themovement distance indicating device 10, j=1. The friction-generated heatquantity is found by multiplying the unit angle D by the torque Tmloaded on the bearing, of the disk motor 4. The calculation of the heatquantity E(i) by the heat quantity calculator 16 can always be performedwhile the optical disk apparatus 1 is in operation.

The temperature calculator 20 calculates the predicted temperaturechange value T(k) in accordance with expression (9) immediately before aseek operation (described below). In the case where no seek operation isperformed for an extended period of time, the predicted temperaturechange value T(k) is calculated every constant time interval or when theheat quantity exceeds a prescribed value. In this manner, a temperaturerise of the disk motor 4 can always be controlled at an appropriatetime.

After the predicted temperature change value T(k) is calculated, the CPU25 initializes the heat quantity E(k) to 0. This initialization preventsthe accumulated heat quantity E from becoming too large and thusprevents the digital value of the heat quantity E from being saturated.

The initialization of the optical disk apparatus 1 is now completed. Theoptical disk apparatus 1 goes into a wait state for a request from thehost apparatus 28 to record or reproduce information. The optical diskapparatus 1 records or reproduces information when receiving such aninstruction from the host apparatus 28.

Hereinafter, a seek operation for transporting the optical head 5 in aradial direction of the optical disk 2 to a prescribed radial positionabove the optical disk 2 so as to perform information recording orreproduction will be described.

When the host apparatus 28 issues a request to record or reproduceinformation, the CPU 25 calculates an intended position at which theinformation recording or reproduction is to be performed. The CPU 25drives the head transporting motor 7 to transport the optical head 5 tothe intended position. Simultaneously, the CPU 25 notifies the commandedcurrent value generator 18 of the intended position. The commandedcurrent value generator 18 calculates a rotation speed of the disk motor4 required at the intended speed as the intended rotation speed.

In the case where the optical disk 2 is of a CLV system, the rotationspeed of the disk motor 4 needs to be changed to the predeterminedintended rotation speed before the seek operation. In this case, a hugeamount of electric current is caused to flow through the disk motor 4.When the seek operations are continued for an extended period of time,the temperature of the disk motor 4 rises to an excessively high level.In order to avoid this, the temperature calculator 20 predicts thetemperature change value before the rotation of the disk motor 4 startsaccelerating or decelerating, and the manner of driving the disk motor 4is adjusted based on the result.

Now, a seek operation performed when the temperature change valuepredicted by the temperature calculator 20 is relatively large and whenthe value is relatively small will be described.

FIG. 3 is a timing diagram illustrating an example of a change of therotation speed of the disk motor 4 (FIG. 1) when the predictedtemperature change value is relatively small.

The disk motor 4 is assumed to rotate at a constant speed θa0. Theintended rotation speed θa1, which is higher than the speed θa0 is setto perform recording or reproduction at an inner position of the opticaldisk 2. The rotation of the disk motor 4 is accelerated to the intendedrotation speed θa1. The rotation speed of the disk motor 4 can becalculated by the speed calculator 12. The CPU 25 can determine variousstates of the optical disk apparatus 1 including the rotation speed ofthe disk motor 4, the temperature change in an arbitrary area of theoptical disk apparatus 1 and the operation of the optical head 5. Then,the CPU 25 can issue various commands to various elements of the opticaldisk apparatus 1. Immediately after the start of the operation of theoptical disk apparatus 1 when the temperature rise is still small andthus the predicted temperature change value T is smaller than athreshold temperature change value Tth, the CPU 25 instructs the currentcontroller 19 not to restrict the driving current. Then, the motordriver 17 receives the maximum commanded current value (Imax) andsupplies the corresponding driving current to the disk motor 4. The diskmotor 4 starts acceleration at the maximum acceleration (period ta1).The transportation of the optical head 5 is simultaneously started.Usually, the time period required to transport the optical head 5 to theintended position is far shorter than the time period required to causethe rotation speed of the disk motor 4 to reach the intended rotationspeed. The optical head 5 reaches the intended position soon after thestart of the seek operation.

The rotation speed of the disk motor 4 gradually increases and reachesthe rotation speed range within which a synchronous clock can begenerated (θa2 to θa1). Then, the synchronous clock generator 23 outputsa synchronous clock. When information reproduction is to be performed,generation of a data signal by the signal processor 24 becomes possibleafter generation of a synchronous clock becomes possible. Thus, theoptical disk apparatus 1 is prepared for reading or reproduction. Afterconfirming that the recording/reproduction is now possible, the CPU 25instructs the current controller 19 to restrict the driving current andnotifies the current controller 19 of a restriction value Ia. Thus, theamount of the current supplied to the disk motor 4 is restricted, whichslows the rise of the rotation speed of the disk motor 4 (period ta2).Since the rotation speed of the disk motor 4 is already in the range inwhich information recording or reproduction is possible (θa2 to θa1),the signal processor 24 can continue recording or reproduction withoutany inconvenience. Since the reduction in the amount of the currentsupplied to the disk motor 4 suppresses heat generation, the temperaturerise can be reduced without adversely influencing the recording orreproduction.

The heat quantity calculator 16 calculates the heat quantity inconsideration of the rotation acceleration of the disk motor 4.Accordingly, even when the value of the current supplied to the diskmotor 4 changes during the seek operation, the heat quantity can stillbe calculated accurately with no influence of the change.

The lower limit of the rotation speed range in which generation of asynchronous clock is possible may be lower than the lower limit θa2 ofthe rotation speed range in which recording or reproduction is possible(θa2 to θa1). For example, the rotation speed range in which generationof a synchronous clock is possible may be the range of θa4 to θa1 shownin FIG. 3. θb4, θc4 and θd4 in FIGS. 4, 8 and 9 described below alsoshow that the lower limit of the rotation speed range in whichgeneration of a synchronous clock is possible may be lower than thelower limit of the rotation speed range In which recording orreproduction is possible.

From the time when the rotation speed of the disk motor 4 reaches thelower limit of the rotation speed range in which generation of asynchronous clock is possible (θa2) and a synchronous clock is generateduntil the time when recording or reproduction is performed, there is atime lag although very short. During the time lag, the disk motor 4continues accelerating. In this example, the driving current isrestricted when the rotation speed of the disk motor 4 reaches the rangein which recording or reproduction is possible. Alternatively, thedriving current is restricted when the rotation speed of the disk motor4 reaches the range in which generation of a synchronous clock ispossible. In this case, the driving current is restricted earlier forthe time lag. Consequently, the heat generation can be furthersuppressed. This manner of restriction is also effective in the casewhere the lower limit of the rotation speed range in which generation ofa synchronous clock is possible is lower than the lower limit of therotation speed range in which recording or reproduction is possible asdescribed above.

In the case where the acceleration or deceleration of the rotation ofthe disk motor 4 is reduced during the seek operation, the operation ofthe signal processor 24 can be more stable until the reproductionstarts. In this manner, the time period required to start reproductionafter the generation of a synchronous clock becomes possible can beshortened.

When the driving current is restricted while the rotation speed of thedisk motor 4 is in the range in which generation of a synchronous clockis possible or in the range in which recording or reproduction ispossible, the time period required for the disk motor 4 to reach theintended rotation speed is extended. While the rotation is accelerated,the time period in which recording or reproduction is performed at a lowrotation speed is extended. Thus, the transfer rate (amount ofinformation recorded or reproduced per unit time) is lowered. Bycontrast, while the rotation speed is decelerated, the time period inwhich recording or reproduction is performed at a high rotation speed isextended. Thus, the transfer rate is raised. On average, the transferrate is not substantially lowered, and only the heat generation issuppressed.

In the case where the rotation speed of the disk motor 4 is already inthe range in which the generation of a synchronous clock is possible orin the range in which recording or reproduction is possible before thestart of the seek operation, the driving current is restrictedimmediately after the start of the seek operation.

For recording and reproduction of information, the rotation speed rangein which the recording or reproduction is possible can be different fromeach other, and thus the time to start restricting the driving currentcan be different from each other. Except for this point, the operationis substantially the same.

In the case where the amount of information requested by the hostapparatus 28 to be recorded or reproduced is small and the informationis completely recorded or reproduced before the rotation speed of thedisk motor 4 matches the intended rotation speed θa1, the motorcontroller 21 changes the intended rotation speed to the rotation speedof the disk motor 4 at the time when the recording or reproduction iscompleted (θa3, end of period ta2) as shown in FIG. 3. Such an operationstops the rise of the rotation speed of the disk motor 4, and the diskmotor 4 continues rotation at the speed θa3. This avoids unnecessaryacceleration or deceleration of the disk motor 4 after the recording orreproduction is completed. As a result, the heat generation in the diskmotor 4 can be suppressed and the temperature rise can be restricted.

In the case where the amount of information requested by the hostapparatus 28 to be recorded or reproduced is excessively large, therotation of the disk motor 4 may be accelerated until the rotation speedof the disk motor 4 matches the intended rotation speed θa1. When therecording or reproduction of the information requested by the hostapparatus 28 is not completed even after the rotation speed of the diskmotor 4 matches the intended rotation speed θa1, the recording orreproduction is continued while the rotation speed is kept at theintended rotation speed of θa1.

The optical disk apparatus 1 may be set so that in the case where therotation of the disk motor 4 is accelerated when the recording orreproduction is completed, the acceleration is continued, and in thecase where the rotation of the disk motor 4 is decelerated when therecording or reproduction is completed, the deceleration is stopped. Insuch a, case, the rotation speed of the disk motor 4 can be kept highand the transfer rate can be increased.

Next, a seek operation performed when the temperature change valuepredicted by the temperature calculator 20 (FIG. 1) is relatively largewill be described.

FIG. 4 is a timing diagram illustrating an example of a change of therotation speed of the disk motor 4 when the predicted temperature changevalue is relatively large.

The disk motor 4 is assumed to be rotating at a constant speed θb0. Theintended rotation speed θb1, which is higher than the speed θb0 is setto perform recording or reproduction above an inner position of theoptical disk 2. The rotation of the disk motor 4 is accelerated to theintended rotation speed θb1. When the predicted temperature change valueT found by the temperature calculator 20 immediately before the seekoperation is larger than the threshold temperature change value Tth, thedriving current is restricted to the commanded current value Ibimmediately after the start of the seek operation, regardless of therotation speed range in which generation of a synchronous clock ispossible (θb2 to θb1). As the predicted temperature change value T islarger, the restriction value Ib is set to be smaller. Thus, the amountof the current supplied to the disk motor 4 is restricted during theseek operation, and therefore the temperature rise can be restricted.

FIG. 5 is a timing diagram illustrating an example of the relationshipbetween the predicted temperature change value and the commanded currentvalue.

In the case where the predicted temperature change value T calculatedimmediately before the start of a seek operation exceeds the thresholdtemperature change value Tth, the restriction value of the drivingcurrent is set to be smaller than the restriction value set for theprevious seek operation in accordance with the difference between thevalues T and Tth. When, for example, seek operations are continued, andthe predicted temperature change value T is slightly lower than thethreshold temperature change value Tth when one seek operation iscompleted and the predicted temperature change value T significantlyexceeds the threshold value Tth when the next seek operation iscompleted, the restriction value of the driving current is set to besmall to restrict the heat generation. When the predicted temperaturechange value T is slightly higher than the threshold temperature changevalue Tth when the next seek operation is completed, the restrictionvalue of the driving current is set to be slightly smaller than thevalue set for the previous seek operation. In this manner, the value Tis kept close to the value Tth.

In FIG. 5, the difference between the value T found immediately beforeone seek operation and the value Tth is ΔT1, and the commanded currentvalue is set to be smaller by a prescribed value (ΔI1). In the casewhere a difference ΔT2 between the value T and the value Tth after asubsequent seek operation is larger than the difference ΔT1, thecommanded current value is set to be smaller by a prescribed value ΔI2,which is larger than ΔI1. Therefore, even when the relationship betweenthe commanded current value and the amount of the current actuallysupplied to the disk motor 4 varies, the temperature change can be keptclose to the threshold temperature change value Tth.

As described above, according to the first example of the presentinvention, the current flowing through the, motor coil 29 of the diskmotor 4 is calculated as J·A(i)/Kt (H is the inertia, and Kt is thetorque constant of the disk motor 4). The torque constant Kt, which isthe proportionality constant between the motor torque and the drivingcurrent, is constant with little dispersion in most of the operationrange of the disk motor 4. Therefore, the acceleration A(i) and theamount of the current are always proportional to each other. Regardlessof the value of the acceleration A(i), the current value can becalculated accurately.

The optical disk 2 generally used is molded at a high precision so as tobe in conformity with predetermined standards. Accordingly, there issubstantially no calculation error of the current value caused by thedispersion in the inertia, except when the disk diameter is different.When the disk diameter is different, the first constant α is changed soas to match the inertia to the disk diameter. Therefore, the currentvalue can always be calculated accurately.

The acceleration A(i) is calculated using the average speed N′(n) whichis obtained by the digital filter 13 from the speed N(n), instead ofusing the speed N(n) calculated based on a pulse which is output by thespeed calculator 12. In this way, even when the pulse output by thespeed calculator 12 includes a large error, the influence of the errorcan be reduced so as to improve the calculation precision of theacceleration A(i). Therefore, the current value can be found accurately.

Regarding the calculation of the heat generation, both the heat quantitygenerated in the motor coil 29 and the friction-generated heat quantitycaused at the bearing of the disk motor 4 are calculated. This improvesthe accuracy of the prediction of the heat quantity of the disk motor 4.

During a seek operation, the restriction value of the driving current ischanged from the value set for the previous seek operation in accordancewith the difference between the predicted temperature change value T(k)and the predetermined threshold temperature change value Tth. Even whenthe input and output gains of the motor driver 17 vary due to thedispersion of various characteristics, the temperature change value canbe kept close to the threshold temperature change value Tth.

When the rotation speed of the disk motor 4 is in the range in whichrecording or reproduction is impossible during a seek operation, therotation of the disk motor 4 is accelerated or decelerated at themaximum acceleration or deceleration. After the rotation speed reachesthe range in which recording or reproduction is possible, the amount ofthe driving current supplied to the disk motor 4 is restricted.Therefore, the heat generation in the disk motor 4 can be suppressedwithout significantly extending the time period required for therotation of the disk motor to reach the range in which recording orreproduction is possible.

When the recording or reproduction is completed while the rotation ofthe disk motor 4 is accelerated or decelerated during the seekoperation, the acceleration or deceleration is stopped on that point.Therefore, the time period in which a huge amount of current is suppliedto the disk motor 4 is prevented from being unnecessarily extended,which prevents unnecessary heat generation.

When the predicted temperature change value T exceeds the thresholdtemperature change value Tth during a seek operation, the restrictionvalue of the driving current is lowered. Thus, a temperature rise can befurther restricted.

In this example, the digital filter 13 calculates the average speedN′(n) from the speed N(n) based on expression (3). Alternatively, theaverage speed N′(n) may be calculated based on, for example, expression(10) shown below.N′(n)=(N(n)+N(n−1) . . . +N(n−m))/m  (10)

In this example, the heat quantity E1(i) generated in the motor coil 29is calculated using the acceleration A(i) as shown in expression (7).Alternatively, the heat quantity E1(i) generated in the motor coil 29may be calculated using, for example, expression (11) shown below.Expression (11) uses, instead of the acceleration A(i), a differentialvalue of the speed which has a significance physically equivalent to theacceleration.E 1(i)=α·(N′(j·i)−N′(j·(i−1))² /Δt(i)  (11)

In this example, the acceleration A(i) is calculated every j'th pulsegenerated by the movement distance indicating device 10. The value of jis not necessarily constant, and may be changed during the operation.

EXAMPLE 2

FIG. 6 is a schematic diagram illustrating a structure of an opticaldisk apparatus 41 according to a second example of the presentinvention.

The optical disk apparatus 41 is different from the optical diskapparatus 1 (FIG. 1) according to the first example in that anacceleration detector (acceleration detection device) 42 of a motorcontrol device 43 of the optical disk apparatus 41 does not include adigital filter. Except for this point, the optical disk apparatus 41 hasthe same structure as that of the optical disk apparatus 1. Identicalelements previously discussed with respect to FIG. 1 bear identicalreference numerals and the descriptions thereof will be omitted.

The acceleration detector 42 operates in the following manner.

The speed calculator 12 and the differential calculator 14 calculate theacceleration A(i) from the speed N(n) of the disk motor 4 by expression(1) shown above and expression (2) shown below, and output theacceleration A(i) to the heat quantity calculator 16.A(i)=(N(j·i)−N(j·(i−1)))/Δt(i)  (2)

In the second example, j is an integer obtained by multiplying thenumber of pulses generated by the movement distance indicating device 10while the disk motor 4 rotates once by an integer. For example, when sixpulses are generated while the disk motor 4 rotates once, j is amultiple of 6. Δt(i) is a time duration from the time when the (j·i)thpulse is generated by the movement distance indicating device 10 untilthe time when the j·(i−1)th pulse is generated by the movement distanceindicating device 10. The predicted temperature change value T(K) iscalculated from the acceleration A(i) in a manner similar to that of thefirst example.

The motor control device 43 and the optical disk apparatus 41 includingthe motor control device 43 operate, for example, in the followingmanner.

The operation is the same as that of the optical disk apparatus 1 untilthe CPU 25 initializes various variables, the disk motor 4 startsrotating, and the speed calculator 12 calculates the speed N(n).

After the speed N(n) found by the speed calculator 12, the accelerationdetector 42 calculates the acceleration A(i) in accordance withexpression (2) using the speed N(n) found by the speed calculator 12. Inexpression (2), j is set to be an integer obtained by multiplying thenumber of pulses which are generated by the movement distance indicatingdevice 10 while the disk motor 4 rotates once as described above.Therefore, the acceleration A(i) can always be found based on the pulseswhich are generated by the same magnetic pole among the plurality ofmagnetic poles of the magnet 31 of the disk motor 4.

For example, it is assumed that the plurality of magnetic poles in themagnet 31 are provided with a positional error, and a pulse generated bya magnetic pole of the magnet 31 having a positional error correspondsto a rotation angle of D+e (e: error component) and the pulse generatednext corresponds to a rotation angle of D−e. When the disk motor 4rotates at a constant speed of N0, the speeds found by expression (1)based on these pulses are represented by expressions (12) and (13),respectively. Both speeds have an error with respect to the actualrotation speed N0.N 0·D/(D+e)  (12)N 0·D/(D−e)  (13)

An acceleration which is calculated based on the speeds found from thesecontinuous pulses has a positive value, although the disk motor 4 isrotated at a constant speed with an acceleration of 0.

However, in this example, the rotation speed is always found based onthe pulses generated by the same, prescribed magnetic pole among theplurality of magnetic poles of the magnet 31, as described above.Therefore, even when the prescribed magnetic pole has a positionalerror, the same positional error is reflected on the pulses. Forexample, when the error component is +e. Therefore, the rotation speedsare calculated based on the pulses corresponding to the rotation angleD+e, the calculated rotation speeds are all equal to a product ofmultiplication of the actual speed by D/(D+e). Accordingly, thedifference in the speed calculated based on these resultant speedsbecomes 0 when the disk motor 4 rotates at a constant speed. Thus, theacceleration can be correctly found to be 0.

As described above, according to the second example, the calculationerror of the acceleration caused by the positional error of magneticpoles can be substantially completely removed by calculating theacceleration based on the pulses which are generated each time the diskmotor 4 rotates an integral number of times (for example, once ortwice).

FIG. 7 is a timing diagram illustrating an example of a change of therotation speed when the disk motor 4 (FIG. 6) is accelerated ordecelerated repeatedly. As shown in FIG. 7, according to the secondexample, even when the actual speed of the disk motor 4 is rapidlyincreased or reduced repeatedly, the acceleration A(i) can be obtainedto substantially match the actual acceleration at a high precision.

When the positional error of the magnetic poles of the magnet 31 of thedisk motor 4 is excessively large, the speed N(n) is processed by a lowpass filter with a reduced cut-off frequency. Thus, the influence of thepositional error can be reduced. However, in this case, when theacceleration of the disk motor 4 is rapidly changed, the calculatedacceleration cannot follow the actual acceleration and a time delay isgenerated as shown in FIG. 7. Especially when the rotation speed issufficiently high to involve the problem of heat generation, theinfluence of the positional error of the magnetic poles appears as alarger error. Accordingly, the cut-off frequency of the low pass filterneeds to be further reduced, which causes a further time delay. Such aninfluence of the positional error of the magnetic poles can besubstantially eliminated by calculating the acceleration based on thepulses which are generated each time the disk motor 4 rotates anintegral number of times (for example, once or twice) as in thisexample. The acceleration detection accompanies a time delaycorresponding to one rotation of the disk motor 4. However, theinfluence of the time delay is reduced at rotation speeds sufficientlyhigh to involve the problem of generation. Therefore, a highly preciseacceleration detection is possible.

Pulses to be used for acceleration detection from among the plurality ofpulses which are generated while the disk motor 4 rotates once can beselected in the following manner. Each time a pulse is generated, thespeeds calculated by expression (1) are averaged for one rotation (orfor an integer number of rotations) of the disk motor 4. Thus, thepulses, based on which the speeds closest to the average speed werefound, are used. In this manner, the speed calculation precision and theacceleration detection precision can further be improved.

The operations of the heat quantity calculator 16 and the temperaturecalculator 20 which are performed based on the detected acceleration arethe same as those in the first example.

Next, a seek operation for moving the optical head 5 in a radialdirection of the optical disk 2 to a desired position above the opticaldisk 2 in order to perform information recording or reproduction will bedescribed.

FIG. 8 is a timing diagram illustrating an example of a change of therotation speed of the disk motor 4 during a seek operation.

When the host apparatus 28 issues a request to record or reproduceinformation, the CPU 25 calculates an intended position at which theinformation recording or reproduction is to be performed. The CPU 25drives the head transporting motor 7 to transport the optical head 5 tothe intended position. Simultaneously, the CPU 25 notifies the commandedcurrent value generator 18 of the intended position. The commandedcurrent value generator 18 calculates a rotation speed of the disk motor4 required at the intended position as the intended rotation speed θc1.

When the predicted temperature change value T calculated by thetemperature calculator 20 is lower than the threshold temperature changevalue Tth and the rotation speed θc0 before the seek operation isoutside the range in in which recording or reproduction is possible (θc2to θc1), the CPU 25 instructs the current driver 19 not to restrict thedriving current. Then, the motor driver 17 receives the maximumcommanded current value (Imax) and thus supplies the correspondingdriving current to the disk motor 4. The disk motor 4 startsacceleration at the maximum acceleration (period tc1).

Next, when the rotation speed of the disk motor 4 reaches θc2 at whichgeneration of a synchronous clock is possible and then at θc2 at whichrecording or reproduction is possible, the commanded current valuegenerator 18 sets the intended rotation speed to θc2 for a prescribedtime period (tc2; for example, about 50 ms). Then, the commanded currentvalue generator 18 re-sets the intended rotation speed to θc1. Thus, thedisk motor 4 once stops accelerating and rotates at a constant speedθc2, and then the rotation of the disk motor 4 is accelerated to therotation speed θc1 (period tc3).

Using such an operation (i.e., once stopping the acceleration ordeceleration of the disk motor 4 when the rotation speed of the diskmotor 4 reaches the range in which recording or reproduction ispossible), the amount of the current flowing through the disk motor 4 istemporarily reduced, thus generating a cooling period. Consequently, thetemperature rise can be restricted.

During period tc3, the current controller 19 restricts the drivingcurrent and thus the commanded current value is restricted to Ic.Therefore, the driving current supplied to the disk motor 4 can bereduced so as to suppress the temperature rise.

Next, with reference to FIG. 9, a seek operation performed when theintended rotation speed is θd1, which is lower than θc1 will bedescribed. FIG. 9 is a timing diagram illustrating an example of achange of the rotation speed of the disk motor 4 during such a seekoperation.

The operations performed during periods td1 and td2 are the same asthose in periods tc1 and tc2 in FIG. 8. In period td3 in which therotation of the disk motor 4 is accelerated in the range in whichrecording or reproduction is possible (θd2 to θd1), the currentcontroller 19 restricts the driving current. At this point, therestriction value Id of the commanded current value set by the currentcontroller 19 varies in accordance with the intended rotation speed(θd1). As the intended rotation speed θd1 is higher, the restrictionvalue of the driving current is set to be large.

For example, the intended rotation speed θc1 in FIG. 8 is higher thanthe intended rotation speed θd1 in FIG. 9. Therefore, the restrictionvalue Ic of the commanded current value in FIG. 8 is larger than therestriction value Id in FIG. 9. Usually, the friction force between theoptical disk 2 and the air, which is generated when the optical disk 2rotates, is higher as the rotation speed is higher. In order to controlthe disk motor 4 to have a high intended rotation speed, a larger motortorque and a larger driving current are necessary than in order tocontrol the disk motor 4 to have a lower intended rotation speed. Whenthe restriction value of the driving current is excessively small, ittakes an excessively long time period to reach the intended rotationspeed, or the rotation speed never reaches the intended speed.Accordingly, during period td3 immediately before the rotation speed ofthe disk motor 4 reaches the intended speed, the restriction value ofthe driving current needs to be larger as the intended rotation speed ishigher. With such setting, whatever the intended rotation speed may be,the rotation speed of the disk motor 4 can reach the intended speed in ashort period of time, and a stable operation is realized.

In this example, after the CPU 25 confirms that the disk motor 4 reachesthe rotation speed range in which recording or reproduction is possible,the current controller 19 restricts the driving current. This operationof the CPU 25 may be omitted. In this case, after the CPU 25 instructsthe intended rotation speed to the commanded current value generator 18,the commanded current value generator 18 calculates the rotation speedrange in which recording or reproduction is possible based on theintended rotation speed, and notifies the current controller 19 of thecalculated range. During a seek operation, the current controller 19monitors the rotation speed of the disk motor 4. When the rotation speedreaches the calculated range, the driving current is restricted. Such anoperation can simplify the control performed by the CPU 25. In addition,this operation makes it possible to determine, before the seek operationis started, whether the rotation speed at that time is within the rangein which recording or reproduction is possible. If the rotation speed iswithin this range, the disk motor 4 rotates at a constant speedimmediately after the seek operation starts. The acceleration ordeceleration of the rotation of the disk motor 4 is started when thetransportation of the optical head 5 is completed. In this manner, theheat generation in the disk motor 4 can significantly be restrictedespecially when seek operations are continuously performed.

As described above, using the operation of stopping the acceleration ordeceleration of the rotation of the disk motor 4 within the rotationspeed range in which recording or reproduction is possible, the timeperiod in which a huge amount of current flows through the disk motor 4can be shortened and thus the heat quantity generated in the disk motor4 can be reduced.

In this example, the upper limit of the range of the commanded currentvalues (Ic, Id) is made constant while the rotation of the disk motor 4is accelerated or decelerated within the rotation speed range in whichrecording or reproduction is possible. Alternatively, the upper limit ofthe range of the commanded current values (Ic, Id) can be set onlyimmediately before the rotation speeds reaches the intended rotationspeed, and the upper limit can be smaller in the remaining period. Inthis case, the heat quantity generated in the disk motor 4 can furtherbe reduced.

As described above, according to the second example of the presentinvention, the acceleration A is calculated when the disk motor 4rotates once or an integral number of times. The acceleration iscalculated based on pulses which are generated by a specific magneticpole of the magnet 31 of the disk motor 4. Thus, the error caused by thepositional error of the magnetic poles can be substantially eliminated.Therefore, the acceleration can be calculated highly precisely with verylittle time delay. As a result, the precision in predicting thetemperature rise can be significantly improved.

During a seek operation, when the rotation speed of the disk motor 4reaches the range in which recording or reproduction is possible, theacceleration or deceleration is stopped for a prescribed time period.Therefore, the heat generation in the disk motor 4 can be suppressedwithout substantially delaying recording or reproduction.

The upper limit (i.e., the restriction value) of the driving currentwithin the rotation speed range in which recording or reproduction ispossible is set to be larger as the intended rotation speed is higher.Accordingly, the rotation speed of the disk motor 4 can be caused toreach a high intended rotation speed in a sufficiently short timeperiod. In the case where the rotation speed of the disk motor 4 iscaused to reach a low intended rotation speed, the temperature rise canbe suppressed.

The CPU 25 and the inertia determiner 26 provided in the motor controldevices 27 and 43 in the first and second examples may be providedoutside the motor control devices 27 and 43.

The acceleration detector 42 preferably calculates the accelerationbased on the pulses which are generated each time the disk motor 4rotates once or an integral number of times. However, pulses which aregenerated each time the motor 4 rotates the number of times obtained bymultiplying one by any number may be used alternatively.

A speed detection device 33 can be structured including the movementdistance indicating device 10, the timer 11, and the speed calculator12. Like the acceleration detector 42 described above, the speeddetection device 33 calculates the speed based on pulses which aregenerated each time the disk motor 4 rotates once or an integral numberof times (for example, once or twice). Accordingly, the speedcalculation error caused by the positional error of the magnetic polescan be eliminated substantially completely.

As described above, a motor control device according to the presentinvention calculates a heat quantity generated in a motor (motor coil29) based on an acceleration of the motor, which is in proportion to adriving current of the motor. Even when the amount of the drivingcurrent changes, the heat quantity can be predicted from the rotationacceleration and thus a temperature change can be predicted at highprecision. Since the motor can be controlled based on the highly precisetemperature prediction, overheating and destruction of the componentscaused by a temperature rise can be prevented.

According to the present invention, the heat quantity is calculatedbased on both the heat quantity of the motor coil, which is found fromthe acceleration, and the friction-generated heat quantity caused by thefriction at the bearing of the motor, which is found from the rotationdistance. Therefore, a motor control device according to the presentinvention can predict a temperature change at higher precision.

An acceleration detection device according to the present inventioncalculates an acceleration of the motor based on the speed of the motoreach time the motor rotates once or an integral number of times.Therefore, the error of the calculation of the acceleration caused by apositional error of the magnetic poles of the magnet of the motor can beeliminated substantially completely. Thus, the acceleration can be foundat high precision.

According to the present invention, even when an optical disk having adifferent diameter is mounted, the heat quantity is calculated from theacceleration based on the difference in inertia among optical diskshaving different diameters. Therefore, a motor control device accordingto the present invention can predict a temperature rise at highprecision.

According to the present invention, when the rotation speed of the motoris within a range in which recording or reproduction is possible, orwhen the predicted temperature change exceeds a prescribed thresholdlevel, the driving current of the motor is restricted. Therefore, anoptical disk apparatus according to the present invention suppresses theheat quantity generated in the motor and thus causes very littletemperature rise.

According to the present invention, the restriction value of the drivingcurrent is changed in accordance with the amount by which thetemperature change exceeds a prescribed threshold level. Therefore, anoptical disk apparatus according to the present invention keeps thetemperature change to equal to or less than the threshold level evenwhen the input and output gains of the motor driver vary.

According to the present invention, when the motor is accelerated ordecelerated while the optical disk apparatus is in a wait state aftercompleting recording or reproduction, the acceleration or decelerationof the motor is stopped. Therefore, the unnecessary operation can beeliminated. Thus, an optical disk apparatus according to the presentinvention causes very little temperature rise.

According to the present invention, when the rotation speed of the motoris in a range in which recording or reproduction is possible, therotation speed is maintained constant for a prescribed period.Therefore, an optical disk apparatus according to the present inventionsuppresses the heat generation and reduces the temperature rise withoutsubstantially delaying the recording or reproduction.

According to the present invention, the upper limit of the range ofcommanded current value for a seek operation is set to be higher as theintended rotation speed increases. Therefore, an optical disk apparatusaccording to the present invention maintains the rotation speed closeeven to a high intended rotation speed. When the intended rotation speedis relatively low, the heat generation is suppressed and the temperaturerise is reduced.

According to the present invention, the magnetic flux of the rotor ofthe motor is performed by the movement distance indicating device(sensor section and waveform rectifier). Such a movement distanceindicating device is usually provided in an apparatus including a motor,the rotation speed of which needs to be detected. In order to calculatethe heat quantity of the motor from the acceleration of the motor, sucha movement distance indicating device can be used. A separatetemperature sensor, current detector or the like is not necessary unlikeconventional apparatuses. According to the present invention, thestructure of the motor can be simplified, and the cost of the componentsand the number of steps of assembly can be reduced.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

1. A disk apparatus, comprising: a motor for rotating a disk; an opticalhead for recording information on the disk or for reproducinginformation from the disk; a motor driver for supplying a drivingcurrent to the motor; a motor controller for setting the drivingcurrent; a speed calculator for calculating a rotation speed of themotor; and a determiner for determining whether or not the rotationspeed of the motor is within a range in which recording of informationto the disk or reproduction of information from the disk by the opticalhead is possible, wherein when the determiner determines that therotation speed of the motor is within the range, the motor controllerrestricts the driving current to a restriction value I_(a).
 2. A diskapparatus, comprising: a motor for rotating a disk; an optical head forrecording information on the disk or for reproducing information fromthe disk; a motor driver for supplying a driving current to the motor; amotor controller for setting the driving current; a synchronous clockgenerator for generating a synchronous clock based on a reproductionsignal which is read from the disk by the optical head; a speedcalculator for calculating a rotation speed of the motor; and adeterminer for determining whether or not the rotation speed of themotor is within a range in which generation of the synchronous clock ispossible, wherein when the determiner determines that the rotation speedof the motor is within the range, the motor controller restricts thedriving current to a restriction value I_(a).
 3. A disk apparatus,comprising: a motor for rotating a disk; an optical head for recordinginformation on the disk or for reproducing information from the disk; amotor driver for supplying a driving current to the motor; a motorcontroller for setting the driving current; a head transporting devicefor transporting the optical head to a prescribed position above thedisk at which recording or reproduction of information is to beperformed by the optical head; a speed calculator for calculating arotation speed of the motor; and a determiner for determining, during aseek operation in which the head is transported, whether or not therotation speed of the motor is within a range in which informationrecording to the disk or information reproduction from the disk by theoptical head is possible, wherein when the determiner determines thatthe rotation speed is within the range, the motor controller restrictsthe driving current to a restriction value I_(a) so that the rotationspeed of the motor is constant for a prescribed time period.